Polishing pad, platen hole cover, polishing apparatus, polishing method, and method for fabricating semiconductor device

ABSTRACT

It is an object of the present invention to provide a windowed polishing pad or a platen hole cover which is used to form planar surfaces in glass, semiconductors, dielectric/metal composites, integrated circuits, etc.; a polishing apparatus including the windowed polishing pad or the platen hole cover; a method for fabricating a semiconductor device using the polishing apparatus; and a polishing method, in which the number of scratches occurring on the surface of the substrate is small, and the polished state can be optically measured satisfactorily during polishing. In order to achieve the above object, a polishing pad is constructed in such a manner that the polishing pad includes a polishing layer and a light-transmissive window member disposed in an opening formed in a part of the polishing layer, wherein the amount of indentation strain measured when a constant load is applied to substantially the entire upper surface of the light-transmissive window member is larger than the amount of indentation strain measured when the same constant load is applied to a region having the same area on the upper surface of the polishing layer.

TECHNICAL FIELD

The present invention relates to a windowed polishing pad which issuitable for use to form planar surfaces in semiconductors,dielectric/metal composites, integrated circuits, etc.; a platen holecover; a polishing apparatus including the windowed polishing pad or theplaten hole cover; and a method for fabricating a semiconductor deviceusing the polishing apparatus.

BACKGROUND ART

As the density of semiconductor devices is increasing, multilevelinterconnections and techniques associated therewith, for example,techniques for forming interlayer insulating films and techniques forforming electrodes using plug processes, damascene processes, or thelike are becoming important. Accordingly, planarization processes forsuch interlayer insulating films and metal films of electrodes are alsobecoming important. As an efficient technique for the planarizationprocesses, a polishing technique referred to as chemical mechanicalpolishing (CMP) is widely used. As disclosed in Japanese UnexaminedPatent Application Publication No. 9-7985, a polishing apparatus usingCMP is receiving attention as an important technique in which, while asubstrate, such as a wafer, is being polished, a laser beam or visiblelight is applied from the back side (platen side) of the polishing padto a surface of the substrate to be polished so that the polished stateis measured. As the polishing pad used for such a polishing apparatus,PCT Japanese Translation Patent Publication No. 11-512977 discloses apolishing pad useful for the polishing of wafers provided withintegrated circuits, at least a portion of the pad being composed of asolid uniform resin sheet with no intrinsic ability to absorb ortransport slurry particles, the resin sheet being transparent to lighthaving a wavelength within the range of 190 to 3,500 nanometers. Thepolishing pad includes a polishing layer and a cushion layer laminatedon the polishing layer with a double-sided adhesive tape or the liketherebetween. An opening is formed at a predetermined position of thepolishing pad, and a window member composed of a transparent soliduniform resin is fitted in the opening. The window member transmitslight so that the surface to be polished can be observed, and preventspolishing slurry from entering the platen hole and getting behind theback of the platen. However, in the polishing pad using such atransparent solid uniform resin for the window member, since the windowmember comes into contact with the surface of the substrate, i.e., thesurface to be polished, scratches easily occur on the surface of thesubstrate, which is problematic. Moreover, since the window member doesnot uniformly come into contact with the surface of the substrate, i.e.,the surface to be polished, the slurry is interposed between the windowmember and the surface of the substrate. As a result, light reflected atthe surface of the substrate is scattered, and it is not possible toachieve satisfactory measurement accuracy, which is also problematic.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a windowed polishingpad or a platen hole cover which is used to form planar surfaces inglass, semiconductors, dielectric/metal composites, integrated circuits,etc.; a polishing apparatus including the windowed polishing pad or theplaten hole cover; a method for fabricating a semiconductor device usingthe polishing apparatus; and a polishing method, in which the number ofscratches occurring on the surface of the substrate is small, and thepolished state can be optically measured satisfactorily duringpolishing.

In order to achieve this object, the present invention has theconstructions described below.

(1) A polishing pad includes a polishing layer and a light-transmissivewindow member disposed in an opening formed in a part of the polishinglayer, wherein the amount of indentation strain (S1) measured under aload W applied to the light-transmissive window member having an upperarea A is larger than the amount of indentation strain (S2) measuredunder a load W applied to a region having the area A at any position onthe upper surface of the polishing layer.

(2) In the polishing pad according to (1), S1/S2≧1.5.

(3) In the polishing pad according to either (1) or (2), thelight-transmissive window member is supported by a highly deformablemember.

(4) In the polishing pad according to (3), the compression modulus ofthe highly deformable member is 0.001 to 0.8 MPa.

(5) In the polishing pad according to any one of (1) to (4), at least apart of the light-transmissive window member is disposed at a positionhigher than the surface of the polishing layer.

(6) In the polishing pad according to any one of (1) to (5), thelight-transmissive window member has a region having a micro rubberA-type hardness of 60 degrees or less and a region having a rubbermicrohardness of 80 degrees or more.

(7) In the polishing pad according to any one of (1) to (6), thelight-transmissive window member has a phase separation structure.

(8) A polishing apparatus includes at least the polishing pad accordingto any one of (1) to (7), means for supplying an abrasive materialbetween the polishing pad and a workpiece, means for making thepolishing pad abut on the workpiece and relatively moving the polishingpad and the workpiece to perform polishing, and means for opticallymeasuring the polished state of the workpiece through thelight-transmissive window member.

(9) A method for fabricating a semiconductor device includes the step ofpolishing a surface of a semiconductor substrate using the polishingapparatus according to (8).

(10) A platen hole cover includes a light-transmissive window member,the platen hole cover being used together with a polishing pad having anopening and fixed on a hole of a platen in a polishing apparatus inwhich the polished state can be optically measured, wherein the amountof indentation strain (S′1) measured under a load W′ applied to theupper surface of the light-transmissive window member having an upperarea A′ is larger than the amount of indentation strain (S′2) measuredunder a load W′ applied to a region having the area A′ at any positionon the upper surface of a polishing layer of the polishing pad usedtogether.

(11) In the platen hole cover according to (10), S′1≧S′2.

(12) In the platen hole cover according to either (10) or (11), thelight-transmissive window member is supported by a highly deformablemember.

(13) In the platen hole cover according to (12), the compression modulusof the highly deformable member is 0.001 to 0.8 MPa.

(14) In the platen hole cover according to any one of (10) to (13), atleast a part of the upper surface of the light-transmissive windowmember is disposed at a position higher than the surface of thepolishing layer of the polishing pad before the start of polishing.

(15) In the platen hole cover according to any one of (10) to (14), thelight-transmissive window member has a region having a micro rubberA-type hardness of 60 degrees or less and a region having a micro rubberA-type hardness of 80 degrees or more.

(16) In the platen hole cover according to any one of (10) to (15), thelight-transmissive window member has a phase separation structure.

(17) A polishing apparatus includes the platen hole cover according toany one of (10) to (16), a polishing pad having an opening engageablewith the platen hole cover, means for supplying an abrasive materialbetween the polishing pad and a surface to be polished, means for makingthe polishing pad abut on the surface to be polished and relativelymoving the polishing pad and the surface to be polished to performpolishing, and means for optically measuring the polished state of aworkpiece through the light-transmissive window member.

(18) A method for fabricating a semiconductor device includes the stepof polishing a surface of a semiconductor substrate using the polishingapparatus according to (17).

(19) A method for polishing a workpiece includes the steps of disposinga polishing pad including a polishing layer, a light-transmissive windowmember which constitutes a part of the polishing pad or which isindependent of the polishing pad on a platen so that the polishing padand the light-transmissive window member can abut against the workpiece;setting the amount of indentation strain (S″1) measured under a load W″applied to the upper surface of the light-transmissive window memberhaving an upper area A″ to be larger than the amount of indentationstrain (S″2) measured under a load W″ is applied to a region having thearea A″ at any position on the surface of the polishing layer of thepolishing pad; and supplying an abrasive material between the polishingpad and the workpiece while the polished state of the workpiece is beingoptically measured through the light-transmissive window member.

In accordance with the present invention, it is possible to provide awindowed polishing pad or a platen hole cover which is used to formplanar surfaces in glass, semiconductors, dielectric/metal composites,integrated circuits, etc.; a polishing apparatus including the windowedpolishing pad or the platen hole cover; a method for fabricating asemiconductor device using the polishing apparatus; and a polishingmethod, in which the number of scratches occurring on the surface of thesubstrate is small, and the polished state can be optically measuredsatisfactorily through the windowed polishing pad or the platen holecover during polishing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view which shows a polishing pad including alight-transmissive window member.

FIG. 2 is a cross-sectional view which shows an example of a structureof a polishing pad including a light-transmissive window member of thepresent invention.

FIG. 3 is a cross-sectional view which shows another example of astructure of a polishing pad including a light-transmissive windowmember of the present invention.

FIG. 4 is a cross-sectional view which shows another example of astructure of a polishing pad including a light-transmissive windowmember of the present invention.

FIG. 5 is a cross-sectional view which shows another example of astructure of a polishing pad including a light-transmissive windowmember of the present invention.

FIG. 6 is a cross-sectional view which shows an example of a platen holecover of the present invention.

FIG. 7 is a side view which shows an embodiment of a polishing apparatuswhich is capable of optically measuring the polished state.

FIG. 8 is a side view which shows another embodiment of a polishingapparatus which is capable of optically measuring the polished state.

FIG. 9 shows an example of a shape of a light-transmissive window memberof the present invention.

REFERENCE NUMERALS

-   -   1 polishing layer    -   2 light-transmissive window member    -   3 polishing pad    -   4 adhesion layer    -   5 cushion layer    -   6 flexible light-transmissive layer in light-transmissive window        member    -   7 highly deformable member    -   8 adhesion layer    -   9 workpiece    -   10 polishing head    -   11 hole    -   12 beam splitter    -   13 light source    -   14 photodetector    -   15 incident light    -   16 reflected light    -   17 platen    -   18 platen hole cover

BEST MODE FOR CARRYING OUT THE INVENTION

Examples of polishing pads of the present invention include a structureincluding a polishing layer and an adhesion member, and a layeredstructure including a polishing layer, a cushion layer, and an adhesionmember.

Any polishing layer which is capable of polishing a workpiece andholding a slurry during polishing may be used. Examples includepolishing layers having rigid foamed structures including closed cells,such as the ones disclosed in PCT Japanese Translation PatentPublication No. 8-500622 and PCT Publication No. 00/12262 pamphlet; apolishing layer having an unfoamed structure including small channelsprovided on the surface which permit the transport of slurry, asdisclosed in PCT Japanese Translation Patent Publication No. 8-511210;and polishing layers having foamed structures including open cellsprepared by impregnating nonwoven fabrics with polyurethanes.

The light-transmissive window member constituting a part of thepolishing pad is fitted in an opening formed in a part of the polishingsurface and constructed so that light can be transmitted from the frontsurface to the back surface of the polishing pad. The light-transmissivewindow member is sufficiently transparent to optical wavelengths inorder to observe and measure the surface of the workpiece with a hazevalue of 90% or less, preferably 70% or less, or more preferably 50% orless. The light-transmissive window member used for the platen holecover of the present invention is fixed so as to cover an opening of aplaten in a polishing apparatus in which the polished state can beoptically measured, and has a haze value of 90% or less, preferably 70%or less, and more preferably 50% or less. That is, thelight-transmissive window member is defined as a member which has a hazevalue of 90% or less, preferably 70% or less, and more preferably 50% orless. Although the lower limit of the haze value is not particularlyset, light-transmissive window members with a haze value of about 0.01%or more are usually advantageous in view of the possibility ofindustrial production.

Herein, the haze value is defined by the following equation: Haze value(%)=(diffuse transmittance/total transmittance)×100. As the haze valueis decreased, the amount of transmitted light is increased, and theamount of radiation of light to the substrate is increased, which isdesirable. The opening in the polishing layer preferably has a slightlylarger area than that of the light-transmissive window member so thatthe light-transmissive window member can be fitted into the opening.FIG. 1 shows an example of a structure of a windowed polishing pad ofthe present invention which includes a polishing layer and alight-transmissive window member fitted in an opening formed in a partof the polishing layer in order to optically measure the polished state.

In the windowed polishing pad including the light-transmissive windowmember of the present invention, the amount of indentation strain (S1)measured when a load W is applied to the light-transmissive windowmember having an upper area A is larger than the amount of indentationstrain (S2) measured when a load W is applied to a region having thearea A at any position on the upper surface of the polishing layer.Herein, the upper area corresponds to the apparent area of the exposedlight-transmissive window member in the polishing layer. That is, theupper area corresponds to the projected area of the exposed region whenviewed from the top although the upper surface of the light-transmissivewindow member may have various shapes, such as a planar shape and acurved shape. Additionally, even if the light-transmissive window ispartially or entirely covered with a film of another material, such as aconstituent of the polishing layer, the light-transmissive window shouldbe considered as being substantially exposed. The reason for this isthat the film does not substantially affect the amount of indentationstrain when the load is applied.

Since the load W must be uniformly applied to the region to be pressed,ideally, a constant pressure is applied to substantially the entiresurface of the region to be pressed. However, when thelight-transmissive window member has sufficient rigidity, even if aconstant pressure is not necessarily applied to the entire surface,self-evidently, the same effect is achieved as that yielded from thecase when a constant pressure is applied to the entire surface. When theload is applied, any appropriate method may be used. For example, a jigincluding a region with the area A which is brought into contact withthe polishing layer or the light-transmissive window member may be used.

When the amount of indentation strain on the upper surface of thepolishing layer is measured, the region which is affected by thelight-transmissive window member should not be selected arbitrarily.Although the amount of indentation strain can be measured at anyposition, it is proper to calculate the average of the values measuredat any ten positions or the like as a representative physical propertyof the entire polishing layer.

In order to ideally measure the amount of indentation strain at thelight-transmissive window member, using an indenter which hassubstantially the same shape as that of the upper surface of thelight-transmissive window member, an area of at least 80% of the upperarea of the light-transmissive window member, and a substantiallysimilar shape as that of the light-transmissive window member, aconstant pressure is applied while the indenter is brought into contactwith substantially the entire upper surface of the light-transmissivewindow member so as not to be in contact with the polishing layer. Inorder to ideally measure the amount of indentation strain at the surfaceof the polishing layer, using the same apparatus used for measuring theamount of indentation strain at the light-transmissive window member andthe same indenter, the same constant pressure is applied. However, ifthe indenter used for pressing the light-transmissive window member isnot flat, a flat indenter is used for the polishing layer.

As the method for measuring the amount of indentation strain, auniversal material testing machine which is commonly used to measurecompression strain, such as a Universal Testing Machine Model 1185 orModel 5565 manufactured by Instron Corporation, may be used. The load Wis selected from the range of 100 g to 8,000 g, and usually, a loadwhich generates a pressure of 0.005 to 0.15 MPa is selected. Such arange corresponds to the range of the pressure applied from the surfaceto be polished to the upper surface of the light-transmissive windowmember or the upper surface of the polishing layer during actualpolishing. By selecting the pressure from the same range when the amountof indentation strain is measured, a suitable polishing pad is obtainedunder the actual polishing conditions. The testing rate is set at 0.1mm/min.

The amount of indentation strain is defined as the difference betweenthe strain generated when 10% of a constant load (pressure) is appliedand the strain generated when the constant pressure is applied.

Briefly speaking, the present invention is characterized in that whenthe same pressure is applied to the upper surface of thelight-transmissive window member and the upper surface of the polishinglayer, the amount of indentation strain of the light-transmissive windowmember is larger than that of the polishing layer. In such aconstruction, even if an excessive pressure occurs locally, it ispossible to prevent scratches from occurring on the surface of theworkpiece because the light-transmissive window member is easilyindented.

The amount of indentation strain (S1) at the upper surface of thelight-transmissive window member is preferably 1.2 times or more, morepreferably 1.5 times or more, still more preferably 2.0 times or more,or most preferably 2.5 times or more the amount of indentation strain(S2) at the upper surface of the polishing layer. As the differencebetween the amount of indentation strain of the light-transmissivewindow member and the amount of indentation strain of the polishinglayer is increased, it is possible to decrease the number of scratchesoccurring on the surface of the workpiece. Examples of specificstructures of the polishing pad which is constructed so that the amountof indentation strain at the upper surface of the light-transmissivewindow member is larger than the amount of indentation strain at theupper surface of the polishing layer are described below.

FIG. 2 shows an example of a structure which includes a double-layerpolishing pad including a cushion layer and a polishing layer. Alight-transmissive window member is provided on the polishing pad. Thelight-transmissive window member is supported by a highly deformablemember disposed on the cushion layer. In this structure, since thehighly deformable member is easily deformed in response to theindentation force, it is possible to set the amount of indentationstrain of the light-transmissive window member to be larger than theamount of indentation strain of the polishing layer.

FIG. 3 shows an example of a structure which includes a double-layerpolishing pad including a cushion layer and a polishing layer. Alight-transmissive window member is provided on the polishing pad. Thelight-transmissive window member is supported by a highly deformablemember disposed on an adhesive layer disposed on the bottom. Since thethickness of the highly deformable member is larger than that of thehighly deformable member shown in FIG. 2, it is possible to set theamount of indentation strain of the light-transmissive window member tobe much larger than the amount of indentation strain of the polishinglayer.

FIG. 4 shows an example of a structure which includes a double-layerpolishing pad including a cushion layer and a polishing layer. Alight-transmissive window member is provided on the polishing pad. Thethickness of the cushion layer at the portion supporting thelight-transmissive window member is larger than the thickness of thecushion layer at the portion supporting the polishing layer. In thisstructure, it is possible to set the amount of indentation strain of thelight-transmissive window member to be larger than the amount ofindentation strain of the polishing layer.

FIG. 5 shows an example of a structure which includes a single-layerpolishing pad. A light-transmissive window member is provided on thepolishing pad. The light-transmissive window member is supported by ahighly deformable member disposed on an adhesive layer disposed at thebottom. It is possible to set the amount of indentation strain of thelight-transmissive window member to be larger than the amount ofindentation strain of the polishing layer.

The highly deformable member is defined as a member which is more easilydeformed compared with the polishing layer or the cushion layer. Beingeasily deformed means having a large deformation in the same shape (inwhich additive properties, linearity, etc., may also be considered, ifnecessary) under the same compressive stress (pressure). As such amember, a foamed sheet is preferably used because of its largedeformation and high deformation recovery. Preferably, a highlydeformable member having a compression modulus of 0.001 to 0.8 MPa isused. By using such a highly deformable member, the pressure temporarilyapplied to the light-transmissive window member can be efficientlyabsorbed. Therefore, scratches can be substantially prevented fromoccurring on the surface of the workpiece. Since the highly deformablemember must be firmly bonded to the light-transmissive window member, afoam-type adhesive tape in which a foamed sheet is used as a base andadhesion layers are provided on both sides of the base is preferablyused. Specific examples thereof include acrylic foam structural adhesivetapes Y-4950, Y-4930, Y-4920, Y-4914, Y-4627, Y-4630F, Y-4609, Y-4615,Y-4604, Y-4608, Y-4612, Y-4620, etc., manufactured by Sumitomo 3M Ltd.,and double-sided tapes 7840 (0.4 white), 7840 (0.6 white), 782 (0.8),etc., manufactured by Teraoka Seisakusho Co., Ltd. The foamed sheet ispreferably composed of closed cells because it must prevent the entry ofpolishing slurry. Preferred examples of such a foamed sheet include EPTsponge manufactured by Daiwabo Co., Ltd., such as EPT#120, EPT#140,EPT#300, EPT#310, EPT#320, and EPT#450.

The thickness and shape of the highly deformable member may be adjustedappropriately depending on the hardness and deformability of thepolishing layer, the cushion layer, or the light-transmissive windowmember.

The platen hole cover of the present invention includes alight-transmissive window member fixed on a hole of a platen in apolishing apparatus in which the polished state can be opticallymeasured; a member for supporting the light-transmissive window member;and means for fixing the light-transmissive window member on the platen.The platen hole cover is a member which covers the entire surface of thehole opened in the platen so that light can be transmitted, which isused together with a polishing pad having an opening, which prevents theentry of polishing slurry, and which transmits measuring light. Theplaten hole cover of the present invention is characterized in that theamount of indentation strain (S′1) measured when a load W′ is applied tothe light-transmissive window member having an upper area A′ is largerthan the amount of indentation strain (S′2) measured when a load W′ isapplied to a region having the area A′ at any position on the uppersurface of the polishing layer of the polishing pad used together.

Herein, the upper area A′ of the light-transmissive window member isdefined as in the upper area A in the polishing pad of the presentinvention described above. The upper area corresponds to the apparentarea of the light-transmissive window member when viewed from the top.That is, the upper area corresponds to the projected area when viewedfrom the top.

The load W′, application of the load, measurement of the amounts ofindentation strain (S′1, S′2), and other preferred constructions can beconsidered as in the polishing pad described above.

In the present invention, the amount of indentation strain at the uppersurface of the light-transmissive window member of the platen hole coveris larger than the amount of indentation strain at the upper surface ofthe polishing layer. In such a construction, even if an excessivepressure occurs locally, it is possible to prevent scratches fromoccurring on the surface of the workpiece because the light-transmissivewindow member is easily indented.

Specific examples will now be described below. The load applied to theplaten hole cover including the light-transmissive window member ispreferably in the range of 100 to 8,000 g. Such a range corresponds tothe range of the constant load applied from the surface to be polishedto the upper surface of the light-transmissive window member or theupper surface of the polishing layer during actual polishing. Byselecting the constant load from the same range when the amount ofindentation strain is measured, a suitable platen hole cover is obtainedunder the actual polishing conditions, which is desirable. In the platenhole cover of the present invention, under the constant load selectedfrom the range of 100 to 8,000 g, the amount of indentation strain atthe upper surface of the light-transmissive window member is preferably1.5 times or more, more preferably 2.0 times or more, or most preferably2.5 times or more the amount of indentation strain at the upper surfaceof the polishing layer. As the difference between the amount ofindentation strain at the upper surface of the light-transmissive windowmember of the platen hole cover and the amount of indentation strain atthe upper surface of the polishing layer is increased, it is possible todecrease the number of scratches occurring on the surface to bepolished. FIG. 6 shows a specific example of the structure of the platenhole cover in which the amount of indentation strain at the uppersurface of the light-transmissive window member is larger than theamount of indentation strain at the upper surface of the polishinglayer. In this structure, the light-transmissive window is supported bya highly deformable member. The highly deformable member has a hole inthe center and can be bonded to the platen so as to cover the platenhole, thereby preventing a polishing slurry from entering the platenhole. The platen hole cover can be bonded to the platen independently ofthe polishing pad. When the polishing pad is replaced at the end of itslife, if the platen hole cover is not damaged, the platen hole cover canbe used continuously, which is advantageous. As the highly deformablemember, the same materials described above may be used.

The light-transmissive window member will be described in more detailbelow. The light-transmissive window member of the windowed polishingpad and the light-transmissive window member of the platen hole covercan be composed of the same material and can have the samecharacteristics.

The light-transmissive window member used in the present inventionpreferably has a region having a micro rubber A-type hardness of 60degrees or less (also referred to as flexible light-transmissive layer)and a region having a micro rubber A-type hardness of 80 degrees or more(also referred to as rigid light-transmissive layer) in view of the factthat scratches can be more successfully prevented from occurring andthat, since a slurry is not interposed between the surface of thelight-transmissive window member and the surface to be polished duringpolishing, the polished state can be optically measured satisfactorily.The flexible light-transmissive layer is preferably provided in theoutermost region of the polishing layer, i.e., in the outermost regionon the surface to be polished. The flexible light-transmissive layer andthe rigid light-transmissive layer may be laminated on each other.Alternatively, a structure whose hardness gradually changes or astructure in which domains of individual regions are distributed may beacceptable.

Herein, the micro rubber A-type hardness will be described. Thishardness is defined as a value measured with a rubber microhardnessdurometer MD-1 manufactured by Kobunshi Keiki Co., Ltd. The rubbermicrohardness durometer MD-1 can measure the hardness of thin/smallspecimens that are difficult to measure with conventional hardnessdurometers. The rubber microhardness durometer MD-1 is designed andmanufactured as a model reduced to about ⅕ of a spring-system rubberhardness durometer A. The value measured with the rubber microhardnessdurometer MD-1 corresponds to the hardness measured with thespring-system rubber hardness durometer A. The rubber microhardnessdurometer MD-1 includes a cylindrical indenter point with a diameter of0.16 mm and a height of 0.5 mm. Loading is performed with a cantileverleaf spring, and the spring load is 2.24 mN at 0 point and 33.85 mN at100 point. The indenter point is controlled with a stepping motor at adescending rate of 10 to 30 mm/sec to perform measurement. Each of theflexible light-transmissive layer and the rigid light-transmissive layerhas a thickness of less than 5 mm, which is too thin to be evaluatedwith the spring-system rubber hardness durometer A. Therefore, therubber microhardness durometer MD-1 is used for evaluation.

The micro rubber A-type hardness of the flexible light-transmissivelayer is preferably 50 degrees or less and more preferably 40 degrees orless. Although the lower limit is not particularly set, a flexiblelight-transmissive layer with a micro rubber A-type hardness of about 10degrees or more is preferably used from a practical standpoint. When theflexible light-transmissive layer is brought into contact with asubstrate, it is deformed at the surface of the substrate because of itssoftness, and a wide region of the flexible light-transmissive layer isin contact with the surface of the substrate. The slurry interposedbetween the flexible light-transmissive layer and the substrate iseasily discharged from the contact area, and measuring light is noteasily scattered by the slurry. Consequently, the polished state can bemeasured satisfactorily. Since the flexible light-transmissive layer issoft, scratches can be prevented from occurring on the surface of thesubstrate.

By combining the flexible light-transmissive layer with the rigidlight-transmissive layer, when the flexible light-transmissive layer isbrought into contact with the substrate, the back of the flexiblelight-transmissive layer is supported by the rigid light-transmissivelayer, and the surface of the light-transmissive window member is easilypressed against the surface of the substrate. The surface of theflexible light-transmissive layer is deformed, and a wider region of theflexible light-transmissive layer is in contact with the surface of thesubstrate. The slurry interposed between the flexible light-transmissivelayer and the substrate is easily discharged from the contact area, andscattering of light does not easily occur. Consequently, measurement canbe performed more satisfactorily.

Specific examples of materials for the flexible light-transmissive layerinclude transparent rubbers and transparent gels. By using suchmaterials, the surface of the flexible light-transmissive layer is veryrapidly deformed when it is in contact with the substrate, and therebythe slurry is discharged efficiently, which is desirable. Specificexamples of transparent rubbers include silicone rubbers and flexiblepolyurethane rubbers. A silicone rubber is prepared by reacting apolydimethylsiloxane main chain with a silane crosslinking agent or thelike. It is possible to freely control the micro rubber A-type hardnessdepending on the molecular weight of the main chain and the amount ofthe crosslinking agent added. It is possible to easily form a flexiblelight-transmissive layer with a micro rubber A-type hardness of 60degrees or less on a rigid light-transmissive layer. Specific examplesof silicone rubbers include SE9185, SE9186, SE9186L, SE9187L, etc.,manufactured by Toray-Dow Corning Silicone Co., Ltd. A polyurethanerubber is prepared by reacting a carbinol-terminated polyether, such aspolyethylene glycol, with an isocyanate crosslinking agent. Bycontrolling the molecular weight of the polyether and the amount of thecrosslinking agent, it is possible to relatively easily form a flexiblelight-transmissive layer with a micro rubber A-type hardness of 60degrees or less on a rigid light-transmissive layer. A gel is defined asa polymer having a three-dimensional network structure which isinsoluble in all liquids or a swollen body of such a polymer. Gels areclassified into hydrogels which are swollen with water and organogelswhich are swollen with organic solvents or organic oligomers. Specificexamples of hydrogels include synthetic polymer gels, such asthree-dimensionally crosslinked poly(vinyl alcohol)s,three-dimensionally crosslinked poly(hydroxyethyl methacrylate),three-dimensionally crosslinked poly(acrylic acid), andthree-dimensionally crosslinked sodium polyacrylate; and natural polymergels, such as agar, gelatin, agarose, and carageenan. Specific examplesof organogels include silicone gels in which silicone rubbers areswollen with silicone oligomers; and polyurethane gels in whichpolyurethane rubbers are swollen with ethylene glycol oligomers or thelike. Among these gels, silicone gels are preferred because a flexiblelight-transmissive layer is relatively easily formed on a rigidlight-transmissive layer.

Examples of materials for the rigid light-transmissive layer with amicro rubber A-type hardness of 80 degrees or more include transparentrigid polymers, such as rigid polyurethanes, poly(methyl methacrylate),polycarbonate, nylons, polyesters, transparent ABS, poly(vinylchloride), poly(vinylidene fluoride), polyether sulfones, polystyrene,polyethylene, polypropylene, and poly(vinyl alcohol)s; and transparentinorganic materials, such as glass, rock crystal, transparent aluminumoxide, and indium titanium oxide.

The flexible light-transmissive layer and the rigid light-transmissivelayer are preferably bonded to each other without an adhesion layertherebetween because light-transmitting properties are not impaired. Thecombination of the material for the flexible light-transmissive layerand the rigid light-transmissive layer is preferably determined inconsideration of adhesive properties of the respective materials. Forexample, when glass is selected for the rigid light-transmissive layer,the flexible light-transmissive layer is preferably composed of aflexible polyurethane rubber, silicone rubber, silicone gel,polyurethane gel, or the like because of satisfactory adhesiveproperties. When a rigid polyurethane is selected for the rigidlight-transmissive layer, the flexible light-transmissive layer ispreferably composed of a flexible polyurethane rubber, polyurethane gel,or the like because of satisfactory adhesive properties. When a nylon isselected for the rigid light-transmissive layer, the flexiblelight-transmissive layer is preferably composed of a synthetic polymergel, such as three-dimensionally crosslinked poly(vinyl alcohol)s andthree-dimensionally crosslinked poly(hydroxyethyl methacrylate) becauseof satisfactory adhesive properties.

In another preferred example, the light-transmissive window member has aphase separation structure. Such a construction can be prepared using atransparent resin having a phase separation structure. As thetransparent resin having a phase separation structure, a transparentresin composition having a heterogenous structure in which differentpolymers form multiple phases selected from multicomponent resincompositions prepared by blending at least two polymers or (co)polymersis preferred. A transparent resin composition prepared by melt-kneadingat least two polymers or (co)polymers is more preferred. Above all, useof a transparent resin composition containing a rubber is preferable inview of the fact that occurrence of scratches due to thelight-transmissive window member can be prevented.

In the light-transmissive window member of the present invention, atransparent resin composition having a heterogenous structure in whichrubber and a transparent resin form separate phases is preferably used.Examples of the morphology thereof include a dispersed domain structurein which rubber particles form a dispersed phase in a transparent resinmatrix, and a lamellar structure including a transparent resin layer anda rubber layer. Among them, a dispersed domain structure in which thecontinuous phase consists of a transparent resin matrix and thedispersed phase consists of rubber particles is preferable. Herein, therubber particles correspond to a polymer or (co)polymer containing arubber polymer as a principal component. The shape of the rubberparticles is not particularly limited, but is preferably globular oroval. Although the size of the rubber particles is not particularlylimited, the number-average particle size of the rubber particles ispreferably 0.1 to 100 μm, more preferably 0.1 to 10 μm, and mostpreferably 0.2 to 5 μm. Additionally, the number-average particle sizeof the rubber particles is determined by digital image analysis ofimages observed with an optical microscope, transmission electronmicroscope, scanning electron microscope, phase-contrast microscope, orthe like.

Preferably, the rubber used in the present invention has a glasstransition temperature of 0° C. or less. Specific examples thereofinclude diene rubbers, such as butadiene rubber, styrene-butadienecopolymers, acrylonitrile-butadiene copolymers, styrene-butadiene blockcopolymers, and butyl acrylate-butadiene copolymers; acrylic rubbers,such as poly(butyl acrylate); and other rubbers, such as natural rubber,grafted natural rubber, natural trans-polyisoprene, chloroprene rubber,polyisoprene rubber, ethylene-propylene copolymers,ethylene-propylene-diene ternary copolymers, ethylene-acryliccopolymers, chlorosulfonated rubber, epichlorohydrin rubber,epichlorohydrin-ethylene oxide copolymers, polyether-urethane rubber,polyester-urethane rubber, nitrile rubber, butyl rubber, siliconerubber, and fluororubbers. Above all, diene rubbers, such as butadienerubber and butadiene copolymers; and olefin rubbers, such asethylene-propylene copolymers and ethylene-propylene-diene ternarycopolymers, are preferable because of their excellent transparency.

The rubber particles are desirably dispersed uniformly in thetransparent resin matrix which is the continuous phase. For thatpurpose, the rubber polymer is preferably grafted with a monomerconstituting the transparent resin matrix, a polymer of the monomer, ora (co)polymer containing the monomer. Alternatively, the rubber polymeris preferably modified with a monomer containing at least one functionalgroup, such as an epoxy group, isocyanate group, acid halide, carboxylicacid group, acid anhydride group, amide group, amino group, imino group,nitrile group, aldehyde group, hydroxyl group, or ester group.

The transparent resin composition usually contains a transparent resinbesides the rubber. As such a transparent resin, either a thermoplasticresin or a thermosetting resin may be used. Above all, in view ofmoldability of the light-transmissive window member, thermoplasticresins are preferable. Specific examples of transparent thermoplasticresins include polyolefin resins; polystyrene resins; polyacrylicresins, such as poly(methyl methacrylate) and polyacrylonitrile;poly(vinyl halide) resins, such as poly(vinyl chloride); poly(vinylidenehalide) resins, such as poly(vinylidene fluoride) and poly(vinylidenechloride); polytetrahalogenated ethylene resins, such aspolytetrafluoroethylene; polyoxyalkylene resins, such aspolyoxymethylene; polyamide resins; polyester resins, such aspolyethylene terephthalate, polybutylene terephthalate, and polyethylenenaphthalate; polycarbonate resins; poly(vinyl alkyl ether) resins, suchas poly(vinyl methyl ether); poly(vinyl acetate) resins; polyurethaneresins; polysulfone resins; poly(phenylene sulfide) resins; andpolyarylate resins. Among them, in view of transparency, polystyreneresins, polyamide resins, polyester resins, and polyolefin resins aremore preferable in the present invention.

The transparent window member of the present invention is preferablycomposed of a transparent resin composition having a heterogenousstructure in which rubber particles are dispersed in the matrix of thetransparent resin. Any transparent resin composition having aheterogenous structure may be used without limitations. Specificpreferred examples include transparent resin compositions having amatrix of a transparent resin prepared by copolymerizing a styrene-basedmonomer with an unsaturated carboxylic acid alkyl ester, and a dispersedphase of rubber particles, such as transparent resin compositionscontaining rubber-reinforced styrene-based resins. Examples thereofinclude transparent high-impact polystyrene (HI-PS), transparent resincompositions containing acrylonitrile-butadiene-styrene copolymers(transparent ABS resins), transparent resin compositions containingacrylonitrile-acrylic rubber-styrene copolymers (transparent AASresins), transparent resin compositions containingacrylonitrile-ethylene propylene rubber-styrene copolymers (transparentAES resins), transparent resin compositions containing methylmethacrylate-butadiene-styrene copolymers (transparent MBS resins), andtransparent resin compositions containing acrylonitrile-chlorinatedpolyethylene-styrene copolymers (transparent ACS resins). Examples oftransparent resin compositions having a polyolefin resin matrix and adispersed phase of rubber particles include transparent resincompositions in which olefin rubbers are dispersed inpolyethylene-containing resins, transparent resin compositions in whicholefin rubbers are dispersed in polypropylene-containing resins, andtransparent resin compositions in which olefin rubbers are dispersed inpolypropylene-polyethylene copolymer-containing resins. Examples oftransparent resin compositions having a polyamide resin matrix and adispersed phase of rubber particles include transparent resincompositions in which maleic anhydride-modified olefin rubbers aredispersed in polyamide-containing resins. Examples of polyamides includenylon 6, nylon 8, nylon 11, nylon 12, nylon 66, nylon 68, and nylon 610.Examples of transparent resin compositions having a polyester resinmatrix and a dispersed phase of rubber particles include transparentresin compositions in which polyolefin rubbers modified withmethacrylates containing glycidyl groups are dispersed inpolyester-containing resins. Examples of polyesters includepoly(ethylene terephthalate) and poly(butylene terephthalate).Furthermore, transparent resin compositions in whichacrylonitrile-butadiene copolymers are dispersed in poly(vinylchloride)-based resins, and transparent resin compositions in whichbutyl acrylate-styrene copolymers or butyl acrylate-butadiene copolymersare dispersed in acrylic resins, such as poly(methyl methacrylate) mayalso be used. Among these transparent resin compositions, transparentresin compositions containing copolymers of rubber-reinforcedstyrene-based resins and unsaturated carboxylic acid alkyl esters aremore preferably used because they can substantially prevent scratchesfrom occurring and because of their excellent transparency.

Examples of a transparent resin composition (A) having a matrix of atransparent resin prepared by copolymerizing a styrene-based monomerwith an unsaturated carboxylic acid alkyl ester and a dispersed phase ofrubber particles include a structure in which a (co)polymer preparedfrom a styrene monomer, an unsaturated carboxylic acid alkyl estermonomer, a vinyl cyanide monomer, and another vinyl monomercopolymerizable with these monomers is grafted to a rubber polymer; anda structure in which a (co)polymer prepared from a styrene monomer, anunsaturated carboxylic acid alkyl ester monomer, a vinyl cyanidemonomer, and another vinyl monomer copolymerizable with these monomersis not grafted to a rubber polymer. Specifically, preferred is atransparent thermoplastic resin including a graft copolymer (A) preparedby copolymerizing 20 to 90 parts by weight of a monomer mixture of anunsaturated carboxylic acid alkyl ester monomer (a), a styrene monomer(b), a vinyl cyanide monomer (c), and a vinyl monomer (d)copolymerizable with these monomers, under the presence of 10 to 80parts by weight of a rubber polymer; and 0 to 90 parts by weight of avinyl copolymer (B) composed of an unsaturated carboxylic acid alkylester monomer (a), a styrene monomer (b), a vinyl cyanide monomer (c),and a vinyl monomer (d) copolymerizable with these monomers, the rubberpolymer content being 5 to 30 percent by weight, in view of the factthat scratches are prevented from occurring and high transparency isachieved.

As the rubber polymer (a1), a rubber polymer having a glass transitiontemperature of 0° C. or less is suitable, and diene rubbers arepreferably used. Specific examples include diene rubbers, such aspolybutadiene, styrene-butadiene copolymers, acrylonitrile-butadienecopolymers, styrene-butadiene block copolymers, and butylacrylate-butadiene copolymers; acrylic rubbers, such as poly(butylacrylate); polyisoprene; and ethylene-propylene-diene ternarycopolymers. Above all, polybutadiene or butadiene copolymers areparticularly preferable.

The rubber particle size of the rubber polymer is not particularlylimited. The weight-average particle size of the rubber particles ispreferably 0.1 to 10 μm and more preferably 0.2 to 5 μm. Additionally,the weight-average particle size of rubber particles may be determinedby a sodium alginate method described in “Rubber Age Vol. 88 p. 484-490(1960) by E. Schmidt, P. H. Biddison”, in which using the phenomenonthat the particle size of creaming polybutadiene particles variesdepending on the sodium alginate concentration, the particle size at anaccumulative fraction of 50% is determined based on the weightpercentage of the creamed portion and the accumulative weight fractionof the sodium alginate concentration. Furthermore, the number-averageparticle size of the rubber particles may be determined by digital imageanalysis of images observed with an optical microscope, transmissionelectron microscope, scanning electron microscope, or phase-contrastmicroscope.

In the light-transmissive window member of the present invention, thetransparent resin composition having the phase separation structure isdisposed in the outermost region on the polishing surface. As long asthe resin composition is disposed in the outermost region on thepolishing surface, a single layer composed of the resin composition or alaminate including the resin composition and other resin or inorganicmaterial may be used. A material having a compositional gradient mayalso be used.

In the present invention, the light-transmissive window member may befabricated by a method in which a mixture of a transparent resin matrixand rubber particles, a composition obtained by melt-kneading a materialprepared by polymerization of a transparent resin in the presence ofrubber particles with a hot blender or extruder in advance, or a mixtureprepared by mixing a transparent resin matrix and rubber particles witha mill is formed into a resin sheet using an injection molding machine,injection press, or extruder; and as necessary, the resin sheet is cutinto a predetermined size.

Preferably, at least a part of the light-transmissive window member isdisposed at a position higher than the surface of the polishing layerwhen the light-transmissive window member is not in contact with thesubstrate. When the region (the outermost surface, in particular)disposed higher than the surface of the polishing layer is composed of aflexible light-transmissive layer, a wide region of the transparentwindow member is brought into contact with the substrate, and the slurryis easily discharged from the contact area, thereby facilitatingobservation of the polished state. Since the surface of thelight-transmissive window member abuts against and moves relatively tothe surface to be polished, stress is easily concentrated at theboundary between the light-transmissive window member and the polishinglayer. Consequently, if the end of the light-transmissive window memberis placed higher than the surface of the polishing layer, thelight-transmissive window member is susceptible to impact. Therefore, asshown in FIGS. 2 to 6, by placing the center of the surface of thelight-transmissive window member higher than the surface of thepolishing layer, and by placing the edge of the light-transmissivewindow member lower than the surface of the polishing layer, the impactat the time of contact with the workpiece is substantially reduced, andthe contact area with the substrate at the center though which lightpasses can be increased, thus enabling satisfactory polishing andsatisfactory measurement.

The thickness of the light-transmissive window member is determined inconsideration of the position at which the light-transmissive windowmember is fixed and the positional relationship with the surface of thepolishing layer. Preferably, the flexible light-transmissive layer has athickness of 0.1 mm or more in view of the fact that a sufficientlylarge area of the surface of the flexible light-transmissive layer canbe brought into contact with the surface of the substrate and thatscratches do not easily occur on the substrate. Preferably, the rigidlight-transmissive layer has a thickness of 0.1 mm or more in view ofthe fact that the rigid light-transmissive layer can support theflexible light-transmissive layer so that a sufficiently large area ofthe surface of the flexible light-transmissive layer is brought intocontact with the substrate. The size of the light-transmissive windowmember is determined depending on the apparatus in which, while asubstrate, such as a wafer, is being polished, a laser beam or visiblelight is applied from the back side (platen side) of the polishing padto a surface of the substrate to be polished so that the polished stateis measured.

Preferably, a light-scattering layer or antireflection layer is providedon the back surface of the light-transmissive window member of thepresent invention so that measuring light from the back of the platen isnot directly reflected in view of satisfactory measurement. In order toform the light-scattering layer, for example, a method in which the backsurface of the light-transmissive window member is roughened bysandblasting, etching with an agent, or the like, or a method in whichthe back surface of the light-transmissive window member is coated witha solution containing silica gel with a particle size of about 1 to 30μm may be employed. In order to form the antireflection layer, forexample, a method may be employed in which a film having a lowerrefractive index than the back surface of the light-transmissive windowmember is formed by wet coating, dry coating, such as vacuum deposition,or the like so that the optical thickness is ¼ or an odd multiple ofoptical wavelengths, thereby achieving the minimum reflectance, i.e.,the maximum transmittance. Herein, the optical thickness is defined as aproduct of the refractive index of a film and the thickness of the film.The antireflection layer may be single-layered or multi-layered. In viewof the refractive index, antireflective properties, and adhesiveproperties of the back surface of the light-transmissive window member,an optimum combination is determined. By forming an antireflectionlayer, the measurement can be carried out accurately, thus enablinghighly accurate processing, which is desirable.

In order to fabricate the light-transmissive window member of thepresent invention, a method in which forming is carried out by pouring athermosetting resin into a metal mold, or a method in which athermoplastic resin is formed into a sheet with a predeterminedthickness by extrusion may be used. In order to fabricate alight-transmissive window member including a flexible light-transmissivelayer and a rigid light-transmissive layer, a method in which a rigidlight-transmissive layer is formed using a transparent material with amicro rubber A-type hardness of 80 degrees or more, a viscous precursorfor forming a flexible light-transmissive layer with a micro rubberA-type hardness of 60 degrees or less is applied to the rigidlight-transmissive layer and allowed to react on the rigidlight-transmissive layer to form the flexible light-transmissive layer,and then the resultant laminate is cut into a predetermined size; or amethod in which a viscous precursor for forming a flexiblelight-transmissive layer is poured into a mold with a predeterminedshape, and a sheet for forming a rigid light-transmissive layer isbrought into contact with the viscous precursor at the opening of themold to cause a reaction may be used.

The polishing apparatus of the present invention includes at least thepolishing pad described above, means for supplying a slurry between thepolishing pad and a workpiece, means for making the polishing pad abuton the substrate and relatively moving the polishing pad and thesubstrate to perform polishing, and means for optically measuring thepolished state through the light-transmissive window member. The meansother than the polishing pad may be constructed by combiningconventionally known means. By using such an apparatus, applying a loadbetween the polishing pad and the substrate while a slurry is interposedbetween the polishing pad and the substrate, and relatively moving thesubstrate and the polishing pad, the workpiece can be polished. Byirradiating the workpiece with light, the polished state of theworkpiece can be optically measured.

Specifically, FIG. 7 shows an example of a structure of an apparatusincluding a windowed polishing pad. A hole 11 is formed in a platen 17,and the polishing pad is disposed so that a light-transmissive windowmember 2 lies on the hole 11. The position of the hole 11 is determinedso that a workpiece 9 held by a polishing head A can be observed whilethe platen 17 is rotated. A light source 13 is placed below the platen17 and is fixed at a position which allows incident light 15 emittedfrom the light source 13 to pass through the hole 11 of the platen 17and the window member 2 and hit the surface of the workpiece 9.Reflected light 16 from the surface of the workpiece 9 is guided to aphotodetector 14 by a beam splitter 12. By analyzing the intensitywaveform of the light detected by the photodetector 14, the polishedstate of the surface of the workpiece can be measured. FIG. 8 shows anexample of a structure of an apparatus including a platen hole cover. Ahole 11 is formed in a platen 17, and the platen hole 11 is covered witha platen hole cover including a light-transmissive window member and ahighly deformable member. A polishing pad having an opening is attachedto the platen 17 such that the platen hole cover is fitted in theopening in the polishing pad.

In accordance with the present invention, by using the windowedpolishing pad or by using the platen hole cover and the polishing pad,and by using an abrasive material (which is preferably a slurry), e.g.,a silica-based slurry, aluminum oxide-based slurry, or ceriumoxide-based slurry, it is possible to locally planarize the insulatingfilms and metal interconnections on semiconductor wafers, to performglobal leveling, or to prevent dishing. Specific examples of the slurryinclude, but are not limited to, CAB-O-SPERSE SC-1 for CMP, CAB-O-SPERSESC-112 for CMP, SEMI-SPERSE AM100 for CMP, SEMI-SPERSE AM100C for CMP,SEMI-SPERSE 12 for CMP, SEMI-SPERSE 25 for CMP, SEMI-SPERSE W2000 forCMP, and SEMI-SPERSE W-A400 for CMP manufactured by CabotMicroelectronics Corporation.

The windowed polishing pad or the combination of the platen hole coverand the polishing pad of the present invention is used, for example, forthe surfaces of insulating layers or metal interconnections formed onsemiconductor wafers. Examples of insulating layers include shallowtrench isolation structures used for interlayer insulating films formetal interconnections and underlayer insulating films for metalinterconnections, and used for isolation. Metal interconnections arecomposed of aluminum, tungsten, copper, or the like, and arestructurally formed, for example, by damascene, dual damascene, or plugprocesses. When metal interconnections are composed of copper, barriermetals, such as silicon nitride, are also subjected to polishing.Although insulating films are currently predominantly composed ofsilicon oxide, insulating films composed of low-dielectric-constantmaterials are becoming to be used in view of delay time. In thepolishing pad of the present invention, it is possible to measure thepolished state satisfactorily while preventing scratches from occurringduring polishing. The polishing pad can also be used for polishingmagnetic heads, hard disks, sapphire, etc., besides semiconductorwafers.

In order to prevent hydroplaning, the surface of the windowed polishingpad or the polishing pad used together with the platen hole cover of thepresent invention may have any shape applicable to conventionalpolishing pads, e.g., a grooved, dimpled, spiral, or concentric shape.

In the windowed polishing pad or the combination of the platen holecover and the polishing pad of the present invention, the surface of thepolishing layer is usually subjected to dressing with a conditioner onwhich diamond abrasive grains are electro-deposited, before or duringpolishing. Either batch dressing performed before polishing or in situdressing performed simultaneously with polishing may be used. Duringdressing, the flexible light-transmissive layer is also ground due tocontact with the conditioner. The flexible light-transmissive layer ispreferably composed of a material that has the same grinding propertiesas those of the polishing layer or that is less easily ground than thepolishing layer because a part of the surface of the flexiblelight-transmissive layer can be always placed at a position higher thanthe surface of the polishing layer and brought into contact with thesurface of the substrate.

It is an object of the present invention to provide a polishing padwhich is used to form planar surfaces in glass, semiconductors,dielectric/metal composites, integrated circuits, etc.; a polishingapparatus including the polishing pad; and a method for fabricating asemiconductor device using the polishing apparatus, in which the numberof scratches occurring on the surface of the substrate is small, and thepolished state can be optically measured satisfactorily duringpolishing.

In the polishing method of the present invention, the upper area A″, theload W″, the amount of indentation strain S″1, and the amount ofindentation strain S″2 can be defined as the same as the upper area A,the load W, the amount of indentation strain S1, and the amount ofindentation strain S2 described with reference to the polishing pad,respectively: The polishing pads and light-transmissive window memberssuitable for use and the specific embodiments of use described above arealso applicable to the polishing method.

EXAMPLES

The present invention will be described in more detail based on theexamples below. In the examples, individual properties were determinedby the methods described below.

1. Indentation strain measuring device: Universal Testing Machine Model1185 manufactured by Instron Corporation

(1) Measurement method: Crosshead measurement

(2) Indenter: An indenter which had an area corresponding to 90% of theupper area of a window member composed of aluminum and which had thesame shape as that of the window member but was not in contact with apolishing layer was specially manufactured and mounted on the UniversalTesting Machine.

(3) Measurement temperature: 23° C.

(4) Testing rate: 0.1 mm/min

(5) Data processing: Data processing system “Merlin” manufactured byInstron Corporation with a data acquisition interval of 100 msec

(6) Amount of indentation strain at constant load: The differencebetween the strain generated when a constant weight (load) was appliedand the strain generated when 10% of the constant weight (load) wasapplied was defined as the amount of indentation strain at the constantload.

(7) Amount of indentation strain at constant pressure: The indentationstrain at a constant pressure was calculated based on the straingenerated when a constant load was applied and the contact area of thepressing jig, and the difference between the indentation strain at theconstant pressure and the indentation strain generated when 10% of theconstant pressure was applied was defined as the amount of indentationstrain at the constant pressure.

2. Micro rubber A-type hardness: Measured with a rubber microhardnessdurometer “MD-1” manufactured by Kobunshi Keiki Co., Ltd. (address:Shimodachiuri Muromachi Nishiiri, Kamigyo-ku, Kyoto).

The construction of the rubber microhardness durometer “MD-1” is asfollows:

2.1 Sensor

(1) Loading system: Cantilever leaf spring

(2) Spring load: 0 point/2.24 gf, 100 point/33.85 gf

(3) Spring load error: ±0.32 gf

(4) Indenter dimensions: Cylindrical with a diameter of 0.16 mm and aheight of 0.5 mm

(5) Displacement detection system: Strain gauge

(6) Pressure foot dimensions: Outer diameter 4 mm, inner diameter 1.5 mm

2.2 Sensor driving unit

(1) Driving system: Vertically driven by a stepping motor. Descendingrate controlled by an air damper.

(2) Vertical stroke: 12 mm

(3) Descending rate: 10 to 30 mm/sec

(4) Height adjustment range: 0 to 67 mm (distance between sample tableand sensor pressure face)

2.3 Sample stand

(1) Sample stand dimensions: Diameter 80 mm

(2) Fine adjustment mechanism: Fine adjustment by XY table andmicrometer head. Stroke: 15 mm for each of X axis and Y axis

(3) Level adjustment mechanism: Main feet for level adjustment and roundspirit level

3. Test wafer for scratch evaluation: 6-inch silicon wafer provided withoxide film (oxide film thickness: 1 μm)

4. Scratch evaluation: For the windowed polishing pad, using a polishingapparatus shown in FIG. 6, polishing was carried out for 2 minutes witha slurry SC-1 manufactured by Cabot Microelectronics Corporation beingsupplied at 200 cc/min while in situ dressing was carried out using aconditioner “CMP-M” manufactured by Asahi Diamond Industrial Co., Ltd.with a compression pressure of 0.04 MPa and at a conditioner rotationalfrequency of 25 rpm. The polishing conditions were as follows: platendiameter: 51 cm, platen rotational frequency: 60 rpm, polishing headrotational frequency: 60 rpm, and polishing pressure: 0.05 MPa. Afterthe polished 6-inch silicon wafer was washed thoroughly, the number ofscratches of 0.5 μm or more was measured with a wafer dust inspectionsystem WM-3 manufactured by Topcon Corporation. For the platen holecover, evaluation was performed using a polishing apparatus shown inFIG. 7 under the same conditions as those described above.

5. Method for checking how satisfactorily light-transmissive windowmember of windowed polishing pad or light-transmissive window member ofplaten hole cover enabled measurement of polished state: Using the waferpolishing apparatus shown in FIG. 6 or 7 and a laser beam of 532 nm,polishing was performed while in situ dressing was carried out using aconditioner “CMP-M” manufactured by Asahi Diamond Industrial Co., Ltd.with a compression pressure of 0.04 MPa and at a conditioner rotationalfrequency of 25 rpm. The polishing conditions were as follows: platendiameter: 51 cm, platen rotational frequency: 60 rpm, polishing headrotational frequency: 60 rpm, and polishing pressure: 0.05 MPa. Whenpolishing was performed under the polishing conditions described abovewhile supplying an aqueous solution of 90 ppm xanthan gum(polysaccharide), which was transparent and had substantially the sameviscosity as that of the slurry, at 200 cc/min, reflected laser lightwas detected by the photodetector, and the intensity of reflected lightwas measured. The ratio of the intensity of reflected light to theintensity of incident light was defined as a blank reflectance. Whenpolishing was performed under the polishing conditions described abovewhile supplying a slurry SC-1 manufactured by Cabot MicroelectronicsCorporation at 200 cc/min, the reflected laser light was detected by thephotodetector, and the intensity of reflected light was measured. Theratio of the intensity of reflected light to the intensity of incidentlight was defined as the reflectance in the presence of slurry. Howsatisfactorily the light-transmissive window member enabled themeasurement of the polished state was indicated by how close thereflectance in the presence of slurry was to the blank reflectance. Asthe amount of slurry interposed between the surface of the window memberand the surface of the substrate increased, the reduction in thereflectance increased.

6. Method for fabricating windowed polishing pad: An IC-1000 polishinglayer manufactured by Rodel Inc. (1.25 mm thick, circular with adiameter of 51 cm) was subjected to a so-called X-Y grooving process(process for forming grooves in a grid shape) in which grooves wereformed at a width of 2.0 mm, a depth of 0.5 mm, and a pitch of 45 mm. Arectangular opening of 19×57 mm was cut out at a predetermined positionof the polishing layer. A rubber sheet (micro rubber A-type hardness: 50degrees) with a predetermined thickness was attached to the polishinglayer with a double-sided adhesive tape, and another double-sidedadhesive tape was attached to the back surface of the rubber sheet. Therubber sheet at the opening of the polishing layer was cut out, the areaof the cut-out portion of the rubber sheet being the same as that of theopening of the polishing layer. A double-sided adhesive tape wasattached to the back surface of the rubber sheet, and a rectangularcutout of 13×50 mm was formed in the double-sided adhesive tape at theopening of the polishing layer/rubber sheet laminate. Alight-transmissive window member which will be described below in eachexample was prepared in advance. A highly deformable member which willbe described below in each example was prepared, the highly deformablemember having an area of 18.5×56.5 mm and having a cutout of 13×50 mm inthe center. The highly deformable member was inserted in the opening ofthe polishing layer/rubber sheet laminate and bonded to the fillet ofthe double-sided adhesive tape disposed at the back surface. Theresultant polishing pad including the light-transmissive window memberwas fixed to a platen of the polishing apparatus shown in FIG. 7 suchthat the hole of the platen and the light-transmissive window member ofthe polishing pad corresponded to each other.

7. Method for fabricating platen hole cover and method for fabricatingpolishing pad having opening which is used together with platen holecover: A light-transmissive window member which will be described belowin each example was prepared in advance. A highly deformable memberwhich will be described below in each example was prepared and adhesivelayers were formed on both sides of the highly deformable member. Acutout of 13×50 mm was formed in the center of the highly deformablemember having an area of 18.5×56.5 mm. The light-transmissive windowmember and the highly deformable member were combined to produce aplaten hole cover. The platen hole cover was attached to the platen ofthe polishing apparatus shown in FIG. 7 so as to cover the entire platenhole. In order to fabricate the polishing pad having an opening whichwas used together with the platen hole cover, an IC-1000 polishing layermanufactured by Rodel Inc. (1.25 mm thick, circular with a diameter of51 cm) was subjected to a so-called X-Y grooving process (process forforming grooves in a grid shape) in which grooves were formed at a widthof 2.0 mm, a depth of 0.5 mm, and a pitch of 45 mm. A rubber sheet(micro rubber A-type hardness: 50 degrees) with a predeterminedthickness was attached to the polishing layer with a double-sidedadhesive tape, and another double-sided adhesive tape was attached tothe back surface of the rubber sheet. An opening of 21×59 mm was formedin the polishing pad at the position corresponding to the platen hole.The polishing pad was attached to the platen such that the platen holecover was placed in the center of the opening of the polishing pad.

Example 1

A transparent window member composed of transparent ABS was prepared bymolding Toyolac 920 (transparent ABS resin) manufactured by TorayIndustries, Inc. at a molding temperature of 60 to 80° C. Thetransparent window member had a thickness of 0.4 mm, a width of 18.5 mm,and a length of 56.5 mm. In the transparent window member, four cornersand four edges of the upper surface were rounded with a radius of 0.4mm. The micro rubber A-type hardness of the light-transmissive windowmember was 99 degrees. A polishing pad was fabricated by bonding an NBRrubber sheet with a thickness of 1 mm to a Rodel IC-1000. An opening of19.5×57.5 mm was formed in the polishing pad at the positioncorresponding to the platen hole. A double-sided tape 442J manufacturedby Sumitomo 3M Ltd. was attached to the rubber sheet side of thepolishing pad having the opening, and a cutout of 13×50 mm was formed inthe double-sided tape in the center of the opening. A highly deformablemember composed of EPT sponge EPT#140 manufactured by Daiwabo Co., Ltd.with a thickness of 1.8 mm was prepared. A double-sided tape 442Jmanufactured by Sumitomo 3M Ltd. was attached to a surface of the highlydeformable member with a size of 18.5×56.5 mm, and a cutout of 13×50 mmwas formed in the center. The cushioning member and the transparentwindow member were laminated on each other, and then the laminate wasbonded to the fillet of the double-sided tape at the back of thepolishing pad having the opening. Thereby, a windowed polishing pad wasprepared. The upper surface of the light-transmissive member of thewindowed polishing pad protruded from the upper surface of the polishinglayer in its periphery by about 0.2 mm. When a weight of 3,740 g wasapplied to the light-transmissive window member with a pressing jighaving a contact area of 17×55 mm, the amount of indentation strain was0.27 mm. When the same weight was applied to the polishing layer withthe same pressing jig, the amount of indentation strain was 0.05 mm.Consequently, the amount of indentation strain at the light-transmissivewindow member was 5.4 times the amount of indentation strain at thepolishing layer. A 6-inch silicon wafer provided with an oxide film waspolished with the windowed polishing pad. The number of scratches wassmall at 17. The blank reflectance during polishing using the aqueoussolution of xanthan gum was 60%. The reflectance during polishing usingthe slurry was 50%, and thus the decrease in the reflectance was small.As is clear from this result, the slurry was not substantiallyinterposed between the light-transmissive window member and the wafer,and satisfactory observation was enabled.

Example 2

A transparent window member composed of transparent ABS was prepared asin Example 1. A highly deformable member composed of EPT sponge EPT#300manufactured by Daiwabo Co., Ltd. with a thickness of 1.7 mm wasprepared. Double-sided tapes 442J manufactured by Sumitomo 3M Ltd. wereattached to both surfaces of the highly deformable member with a size of18.5×56.5 mm, and a cutout of 13×50 mm was formed in the center. Thetransparent window member and the cushioning member were laminated oneach other to form a platen hole cover. A polishing pad was fabricatedby bonding an NBR rubber sheet with a thickness of 1 mm to a RodelIC-1000 and attaching a double-sided tape 442J manufactured by Sumitomo3M Ltd. to the back surface of the rubber. An opening of 21×59 mm wasformed in the polishing pad at the position corresponding to the platenhole. When a weight of 3,000 g was applied to the light-transmissivewindow member of the platen hole cover with a pressing jig having acontact area of 17×55 mm, the amount of indentation strain was 0.15 mm.When the same weight was applied to the polishing layer of the polishingpad with the same pressing jig, the amount of indentation strain was0.04 mm. Consequently, the amount of indentation strain at thelight-transmissive window member was 3.75 times the amount ofindentation strain at the polishing layer. The platen hole cover wasattached to the platen, and the polishing pad was also attached to theplaten such that the platen hole cover was fitted in the opening. Theupper surface of the transparent window member of the platen hole coverprotruded from the upper surface of the polishing layer of the polishingpad by about 0.1 mm.

A 6-inch silicon wafer provided with an oxide film was polished with thepolishing pad and the platen hole cover. The number of scratches wassmall at 10. The blank reflectance during polishing using the aqueoussolution of xanthan gum was 55%. The reflectance during polishing usingthe slurry was 48%, and thus the decrease in the reflectance was small.As is clear from this result, the slurry was not substantiallyinterposed between the light-transmissive window member of the platenhole cover and the wafer, and satisfactory observation was enabled.

Example 3

By polymerization of MMA, a PMMA sheet with a thickness of 0.3 mm wasformed, and the PMMA sheet was coated with one-part silicone SE9185manufactured by Toray-Dow Corning Silicone Co., Ltd. at a thickness of0.3 mm. Thereby, a transparent window member with a thickness of 0.6 mmand a size of 18.5 a 56.5 mm was fabricated. The silicone rubber layerhad a micro rubber A-type hardness of 50 degrees, and the PMMA layer hada micro rubber A-type hardness of 99 degrees. A polishing pad wasfabricated by bonding a foamed polyurethane sheet with a thickness of 1mm and a density of 0.1 to a Rodel IC-1000. An opening of 19.5×57.5 mmwas formed in the polishing pad at the position corresponding to theplaten hole. A double-sided tape 442J manufactured by Sumitomo 3M Ltd.was attached to the foamed polyurethane side of the polishing pad havingthe opening, and a cutout of 13×50 mm was formed in the double-sidedtape in the center of the opening. A highly deformable member composedof EPT sponge #140 manufactured by Daiwabo Co., Ltd. with a thickness of1.6 mm was prepared. A double-sided tape 442J manufactured by Sumitomo3M Ltd. was attached to a surface of the highly deformable member with asize of 18.5×56.5 mm, and a cutout of 13×50 mm was formed in the center.The cushioning member and the transparent window member were laminatedon each other, and the laminate was bonded to the fillet of thedouble-sided adhesive tape disposed at the back surface of the polishingpad having the opening. Thereby, a windowed polishing pad was produced.The upper surface of the light-transmissive window member of thewindowed polishing pad protruded from the upper surface of the polishinglayer in its periphery by about 0.1 mm. When a weight of 1,500 g wasapplied to the light-transmissive window member with a pressing jighaving a contact area of 17×55 mm, the amount of indentation strain was0.11 mm. When the same weight was applied to the polishing layer withthe same pressing jig, the amount of indentation strain was 0.05 mm.Consequently, the amount of indentation strain at the light-transmissivewindow member was 2.2 times the amount of indentation strain at thepolishing layer. A 6-inch silicon wafer provided with an oxide film waspolished with the windowed polishing pad. The number of scratches wassmall at 15. The blank reflectance during polishing using the aqueoussolution of xanthan gum was 45%. The reflectance during polishing usingthe slurry was 38%, and thus the decrease in the reflectance was small.As is clear from this result, the slurry was not substantiallyinterposed between the light-transmissive window member and the wafer,and satisfactory observation was enabled.

Example 4

A light-transmissive window member similar to that in Example 3 wasfabricated. A highly deformable member composed of EPT sponge EPT#140manufactured by Daiwabo Co., Ltd. with a thickness of 1.7 mm wasprepared. Double-sided tapes 442J manufactured by Sumitomo 3M Ltd. wereattached to both surfaces of the highly deformable member with a size of18.5×56.5 mm, and a cutout of 13×50 mm was formed in the center. Thetransparent window member and the cushioning member were laminated oneach other to form a platen hole cover. An opening of 21×59 mm wasformed in a Rodel IC-1000/Suba400 laminated polishing pad at theposition corresponding to the platen hole. When a weight of 2,000 g wasapplied to the light-transmissive window member of the platen hole coverwith a pressing jig having a contact of 17×55 mm, the amount ofindentation strain was 0.14 mm. When the same weight was applied to thepolishing layer of the polishing pad with the same pressing jig, theamount of indentation strain was 0.02 mm. Consequently, the amount ofindentation strain at the light-transmissive window member was 7 timesthe amount of indentation strain at the polishing layer. The platen holecover was attached to the platen, and the polishing pad was alsoattached to the platen such that the platen hole cover was fitted in theopening. The upper surface of the transparent window member of theplaten hole cover protruded from the upper surface of the polishinglayer of the polishing pad by about 0.2 mm. A 6-inch silicon waferprovided with an oxide film was polished with the polishing pad and theplaten hole cover. The number of scratches was small at 17. The blankreflectance during polishing using the aqueous solution of xanthan gumwas 55%. The reflectance during polishing using the slurry was 48%, andthus the decrease in the reflectance was small. As is clear from thisresult, the slurry was not substantially interposed between thelight-transmissive window member and the wafer, and satisfactoryobservation was enabled.

Example 5

A rigid polyurethane sheet with a thickness of 0.25 mm was formed bymixing 300 g of Uniroyal Adiprene L-325, i.e., a polyether-basedurethane polymer, and 76 g of 4,4′-methylene-bis(2-chloroaniline) andpouring the mixture into a mold. The rigid polyurethane sheet had amicro rubber A-type hardness of 95 degrees. A light-transmissive windowmember was fabricated by cutting the rigid polyurethane sheet into asize of 18.5×56.5 mm. Using a polishing pad prepared by bonding a rubbersheet with a thickness of 1 mm to an IC-1000, the light-transmissivewindow member, and acrylic foam adhesive tape Y-4620 manufactured bySumitomo 3M Ltd. as a highly deformable member, a polishing pad providedwith the light-transmissive window member was fabricated. When apressure of 400 g was applied to the light-transmissive window member ofthe polishing pad, the amount of indentation strain was 0.21 mm. Theamount of indentation strain at the polishing layer was 0.06 mm.Consequently, the amount of indentation strain at the light-transmissivewindow member was 3.5 times the amount of indentation strain at thepolishing layer. A 6-inch silicon wafer provided with an oxide film waspolished with the polishing pad provided with the light-transmissivewindow member. The number of scratches was small at 20. The blankreflectance during polishing using the aqueous solution of xanthan gumwas 50%. The reflectance during polishing using the slurry was 40%, andthus the decrease in the reflectance was small. As is clear from thisresult, the slurry was not substantially interposed between thelight-transmissive window member and the wafer, and satisfactoryobservation was enabled.

Example 6

A glass sheet with a thickness of 0.5 mm was prepared. A single-layerantireflection film was formed by vapor deposition of magnesium fluorideon the back surface of the glass sheet. The glass sheet had a microrubber A-type hardness of 100 degrees. The glass sheet was coated withone-part silicone SE9185 manufactured by Toray-Dow Corning Silicone Co.,Ltd. at a thickness of 0.3 mm, and left to stand at 60° C. for 1 hour.The laminate was cut into a size of 18.5×56.5 mm with a diamond cutter,and the silicone rubber was cut with a cutter knife to form alight-transmissive window member with a shape shown in FIG. 7. Theflexible light-transmissive layer had a micro rubber A-type hardness of30 degrees. Using a polishing pad prepared by bonding a rubber sheetwith a thickness of 1.5 mm to an IC-1000, the light-transmissive windowmember, and an acrylic foam adhesive tape Y-4620 manufactured bySumitomo 3M Ltd. as a highly deformable member, a polishing pad providedwith the light-transmissive window member was fabricated. The amount ofindentation strain at the light-transmissive window member of thepolishing pad was 0.21 mm under a pressure of 400 g. The amount ofindentation strain at the polishing layer was 0.06 mm. Consequently, theamount of indentation strain at the light-transmissive window member was3.5 times the amount of indentation strain at the polishing layer. Apolishing pad provided with a light-transmissive window member wasfabricated using the light-transmissive window member, and a 6-inchsilicon wafer provided with an oxide film was polished with thepolishing pad provided with the light-transmissive window member. Thenumber of scratches was small at 5. The blank reflectance duringpolishing using the aqueous solution of xanthan gum was 60%. Thereflectance during polishing using the slurry was 48%, and thus thedecrease in the reflectance was small. As is clear from this result, theslurry was not substantially interposed between the light-transmissivewindow member and the wafer, and satisfactory observation was enabled.

Comparative Example 1

A rigid polyurethane sheet with a thickness of 1.25 mm was formed bymixing 300 g of Uniroyal Adiprene L-325, i.e., a polyether-basedurethane polymer, and 76 g of 4,4′-methylene-bis(2-chloroaniline) andpouring the mixture into a mold. The rigid polyurethane sheet had amicro rubber A-type hardness of 95 degrees. A light-transmissive windowmember was formed by cutting the rigid polyurethane sheet into a size of18.5×56.5 mm. An opening of 19×57 mm was formed in an IC-1000 and arubber sheet with a thickness of 1 mm was bonded to the IC-1000 with adouble-sided tape. A cutout of 13×50 mm was formed in the rubber sheetat the position corresponding to the opening. The light-transmissivewindow member was inserted into the opening and bonded to the fillet ofthe rubber sheet. A polishing pad provided with the light-transmissivewindow member was thereby fabricated. The amount of indentation strainat the transmissive window member of the polishing pad was 0.035 mmunder a pressure of 400 g. The amount of indentation strain at thepolishing layer was 0.07 mm. Consequently, the amount of indentationstrain at the light-transmissive window member was smaller than theamount of indentation strain at the polishing layer. A 6-inch siliconwafer provided with an oxide film was polished with the polishing padprovided with the light-transmissive window member. The number ofscratches was large at 110. The blank reflectance during polishing usingthe aqueous solution of xanthan gum was 55%. The reflectance duringpolishing using the slurry was 15%, and thus the decrease in thereflectance was large. As is clear from this result, a large amount ofthe slurry was interposed between the light-transmissive window memberand the wafer, and satisfactory observation was not performed.

Comparative Example 2

A light-transmissive window member composed of transparent ABS wasformed at a thickness of 1.3 mm and a size of 18.5×56.5 mm. Thelight-transmissive window member had a micro rubber A-type hardness of99 degrees. An opening of 19.5×57.5 mm was formed in a Rodel IC-1000 atthe position corresponding to the platen hole. Double-sided tapes 442Jmanufactured by Sumitomo 3M Ltd. were attached to both surfaces of anNBR rubber sheet with a thickness of 1 mm. The NBR rubber sheet wasbonded to the IC-1000 having the opening. A cutout of 13×50 mm wasformed in the NBR rubber in the center of the opening. Thelight-transmissive window member was fitted in the opening and bonded tothe rubber and the fillet of the double-sided tape. A windowed polishingpad was thereby fabricated. The upper surface of the light-transmissivewindow member of the windowed polishing pad protruded from the polishinglayer in its periphery by about 0.1 mm. When a weight of 3,000 g wasapplied to the light-transmissive window member with a pressing jighaving a contact area of 17×55 mm, the amount of indentation strain was0.05 mm. When the same weight was applied to the polishing layer withthe same pressing jig, the amount of indentation strain was 0.04 mm.Consequently, the amount of indentation strain at the light-transmissivewindow member was 1.25 times the amount of indentation strain at thepolishing layer. A 6-inch silicon wafer provided with an oxide film waspolished with the windowed polishing pad. The number of scratches wassignificantly large at 300. The blank reflectance during polishing usingthe aqueous solution of xanthan gum was 60%. The reflectance duringpolishing using the slurry was 50%, and thus the decrease in thereflectance was small. As is clear from this result, the slurry was notsubstantially interposed between the light-transmissive window memberand the wafer, and satisfactory observation was enabled.

Comparative Example 3

A transparent window member composed of transparent ABS was prepared asin Example 1. An NBR rubber sheet with a thickness of 1.9 mm wasprepared. Double-sided tapes 442J manufactured by Sumitomo 3M Ltd. wereattached to both surfaces of the NBR rubber sheet with a size of18.5×56.5 mm, and a cutout of 13×50 mm was formed in the center. Thetransparent window member and the cushioning member were laminated oneach other to form a platen hole cover. A polishing pad was fabricatedby bonding an NBR rubber sheet with a thickness of 1 mm to a RodelIC-1000 and attaching a double-sided tape 442J manufactured by Sumitomo3M Ltd. to the back surface of the rubber. An opening of 21×59 mm wasformed in the polishing pad at the position corresponding to the platenhole. When a weight of 3,000 g was applied to the light-transmissivewindow member of the platen hole cover with a pressing jig having acontact area of 17×55 mm, the amount of indentation strain was 0.05 mm.When the same weight was applied to the polishing layer of the polishingpad with the same pressing jig, the amount of indentation strain was0.04 mm. Consequently, the amount of indentation strain at thelight-transmissive window member was 1.25 times the amount ofindentation strain at the polishing layer. The platen hole cover wasattached to the platen, and the polishing pad was also attached to theplaten such that the platen hole cover was fitted in the opening. Theupper surface of the transparent window member of the platen hole coverprotruded from the upper surface of the polishing layer of the polishingpad by about 0.1 mm.

A 6-inch silicon wafer provided with an oxide film was polished with thepolishing pad and the platen hole cover. The number of scratches waslarge at 260. The blank reflectance during polishing using the aqueoussolution of xanthan gum was 55%. The reflectance during polishing usingthe slurry was 48%, and thus the decrease in the reflectance was small.As is clear from this result, the slurry was not substantiallyinterposed between the light-transmissive window member of the platedhole cover and the wafer, and satisfactory observation was enabled.

1. A polishing pad comprising a polishing layer and a light-transmissivewindow member disposed in an opening formed in a part of the polishinglayer, wherein the amount of indentation strain (S1) measured under aload W applied to the light-transmissive window member having an upperarea A is larger than the amount of indentation strain (S2) measuredunder a load W applied to a region having the area A at any position onthe upper surface of the polishing layer.
 2. A polishing pad accordingto claim 1, wherein S1/S2≧1.5.
 3. A polishing pad according to eitherclaim 1 or 2, wherein the light-transmissive window member is supportedby a highly deformable member.
 4. A polishing pad according to claim 3,wherein the compression modulus of the highly deformable member is 0.001to 0.8 MPa.
 5. A polishing pad according to any one of claims 1 to 4,wherein at least a part of the light-transmissive window member isdisposed at a position higher than the surface of the polishing layer.6. A polishing pad according to any one of claims 1 to 5, wherein thelight-transmissive window member has a region having a micro rubberA-type hardness of 60 degrees or less and a region having a rubbermicrohardness of 80 degrees or more.
 7. A polishing pad according to anyone of claims 1 to 6, wherein the light-transmissive window member has aphase separation structure.
 8. A polishing apparatus comprising at leastthe polishing pad according to any one of claims 1 to 7, means forsupplying an abrasive material between the polishing pad and aworkpiece, means for making the polishing pad abut on the workpiece andrelatively moving the polishing pad and the workpiece to performpolishing, and means for optically measuring the polished state of theworkpiece through the light-transmissive window member.
 9. A method forfabricating a semiconductor device comprising the step of polishing asurface of the semiconductor substrate using the polishing apparatusaccording to claim
 8. 10. A platen hole cover comprising alight-transmissive window member, the platen hole cover being usedtogether with a polishing pad having an opening and fixed on a hole of aplaten in a polishing apparatus in which the polished state can beoptically measured, wherein the amount of indentation strain (S′1)measured under a load W′ applied to the upper surface of thelight-transmissive window member having an upper area A′ is larger thanthe amount of indentation strain (S′2) measured under a load W′ appliedto a region having the area A′ at any position on the upper surface of apolishing layer of the polishing pad used together.
 11. A platen holecover according to claim 10, wherein S′1≧S′2.
 12. A platen hole coveraccording to either claim 10 or 11, wherein the light-transmissivewindow member is supported by a highly deformable member.
 13. A platenhole cover according to claim 12, wherein the compression modulus of thehighly deformable member is 0.001 to 0.8 MPa.
 14. A platen hole coveraccording to any one of claims 10 to 13, wherein at least a part of theupper surface of the light-transmissive window member is disposed at aposition higher than the surface of the polishing layer of the polishingpad before the start of polishing.
 15. A platen hole cover according toany one of claims 10 to 14, wherein the light-transmissive window memberhas a region having a micro rubber A-type hardness of 60 degrees or lessand a region having a micro rubber A-type hardness of 80 degrees ormore.
 16. A platen hole cover according to any one of claims 10 to 15,wherein the light-transmissive window member has a phase separationstructure.
 17. A polishing apparatus comprising: the platen hole coveraccording to any one of claims 10 to 16; a polishing pad having anopening engageable with the platen hole cover; means for supplying anabrasive material between the polishing pad and a surface to bepolished; means for making the polishing pad abut on the surface to bepolished and relatively moving the polishing pad and the surface to bepolished to perform polishing; and means for optically measuring thepolished state of a workpiece through the light-transmissive windowmember.
 18. A method for fabricating a semiconductor device comprisingthe step of polishing a surface of a semiconductor substrate using thepolishing apparatus according to claim
 17. 19. A method for polishing aworkpiece comprising the steps of: disposing a polishing pad comprisinga polishing layer, a light-transmissive window member which constitutesa part of the polishing pad or which is independent of the polishing padon a platen so that the polishing pad and the light-transmissive windowmember can abut against the workpiece; setting the amount of indentationstrain (S″1) measured under a load W″ applied to the upper surface ofthe light-transmissive window member having an upper area A″ to belarger than the amount of indentation strain (S″2) measured under a loadW″ applied to a region having the area A″ at any position on the surfaceof the polishing layer of the polishing pad; and supplying an abrasivematerial between the polishing pad and the workpiece while the polishedstate of the workpiece is being optically measured through thelight-transmissive window member.